Passive RC Network Research Articles

Active nonreciprocal realisation of the compact symmetrical network for transfer-function synthesis

The well known method of realising a prescribed short-circuit transfer admittance function or open-circuit transfer impedance function (having real- or imaginary-frequency poles with unspecified associated driving-point immittances) as a compact symmetrical lattice is applied to a nonreciprocal form with the advantage of avoiding the lattice-to-ladder conversion problem. An example is given of an open-circuit transfer impedance function having real-frequency poles, requiring LC elements, which (if ideal transformers are ruled out) needs a smaller total amount of L or C than its reciprocal equivalent. In the RC case, Ozaki presented a method of realising a compact symmetrical network in the form of two parallel passive RC networks without the need for the intermediate lattice form. Accordingly, comparison is made between the nonreciprocal and Ozaki's method; two examples are given—one minimum-phase, the other non-minimum-phase—for both of which the nonreciprocal method is found to require substantially fewer passive components.

Design tables for active filters having 2nd- and 4th-order chebȳshev responses in pass and stop bands

The paper presents tables which facilitate the design of low-pass and band-pass RC active filter networks having Chebyshev 2nd- and 4th-order response in both pass and stop bands. The synthesis method used is that due to Yanagisawa. This yields a network containing a current-reversing negative-impedance convertor and passive RC networks to obtain a required voltage transfer function. An optimum polynomial due to Sipress is used in the synthesis, giving the minimum sensitivity of the filter response to errors in the transfer characteristic of the negative-impedance convertor. The design procedure using Zolatarev fractions is outlined, and the method for obtaining required amplitudes of ripple in the pass band is explained. The selection of certain ripple amplitudes requires a change in the network configuration. The Yanagisawa-synthesis procedure is discussed briefly, the use of the design tables is explained and an example is given. Experimental results obtained with 2nd- and 4th-order low-pass filters are shown and are compared with the theoretical curves.

A New Class of FM Subcarrier Oscillators

This paper describes a new class of millivolt-controlled subcarrier oscillators developed especially for operation in the rugged environments of orbital programs. The oscillators cover all the standard IRIG channels. The full IRIG signal-frequency response is achieved at a modulation index equal to five. A less-than-unity-gain, long-tailed pair, silicon-transistor, dc amplifier and a greater-than-unity-gain RC network are combined to form a sine-wave oscillator. The center frequency is deviated ± 15 per cent by a ± 10 millivolt control signal. Excellent linearity characteristics are achieved. A unique feature of the circuit is the inherent deviation limiting. Inductors are avoided in the oscillator design. The passive RC network synthesis procedure is developed to realize 1) a voltage gain greater than unity, 2) the proper percentage of deviation with excellent linearity characteristics, and 3) inherent deviation limiting to contain the FM signal spectra within their assigned channels. The center frequency is deviated by controlling the relative gain of the long-tailed pair type of differential dc amplifier. A pure sine wave is generated without additional filtering. The balanced nature of the circuit yields excellent center frequency stability from 0°C to + 85°C. Center frequency time drift provides an improvement of at least one order of magnitude over present state-of-the-art millivolt-controlled oscillators. Measured data is presented to support the procedures used in the design. The oscillator and associated circuitry are contained in a 4?-cubic-inch package that weighs 4 ounces.

An electrical analogue for heat waves in an exothermic medium

The paper describes the design, construction and operation of an electrical analogue used for simulating the conditions of propagation of heat waves in an exothermic medium.The equipment is in two parts. The first is a passive RC network which is the usual form of analogue for heat conduction problems. The second consists of a function generator which calculates the stored energy released as the wave travels across the medium, together with the necessary switching apparatus. The function generator is switched rapidly along the path of the wave. Its output for any point is a function of the temperature at that point. As the wave reaches a given point, additional energy is released into the network. This modifies the conditions at each point to satisfy equations of the form-δ2ψ+ρdψ/dt = f(ψ)The paper also describes the construction and operation of electronic switches capable of scanning the network and adjusting the conditions in times of the order of 5 millisec per node.

Synthesis of ActiveRCNetworks

A basic theorem is derived for RC networks containing active elements. It is shown that no more than one active element, embedded in a passive RC network, is needed to realize any driving-point function. Sufficiency of only one active element is shown by developing a synthesis method. A synthesis technique for n-port passive RC networks is developed in order to establish the sufficiency proof of the basic theorem. A more practical method of realizing driving-point functions, using active RC networks, termed the “cascade” method, is also presented. This method is applied to the design of a tenth-order Tchebycheff parameter filter.

Synthesis of Passive RC Networks with Gains Greater than Unity

This paper illustrates the fact that three-terminal passive resistor-capacitor networks are capable of having unity voltage gain at zero frequency and higher than unity gain over a prescribed frequency band. A general design procedure for synthesizing a transfer function with these properties using, insofar as possible, known methods of synthesis is outlined. Together with suggestions for further work, two examples are presented to illustrate the method.